1. Field of the Invention
The invention relates to an apparatus and method for controlling the manufacture of magnetic heads.
2. Description of the Prior Art
In the cross-referenced Abbott et al. application, there are discussed the benefits made possible by thin film batch-fabricated magnetic heads. Also discussed are the problems of achieving the small dimensions and tolerances of such heads in a practical manufacturing environment. The solution is described as connecting groups of single-turn head elements deposited on a substrate together with conductive bridges. Electrical conduction through the bridges is monitored during fast rough grinding to the throat height dimension and, after the bridges break, the underlying element conductors are monitored. Grinding continues until the monitored value indicates that the final dimension has been reached. In one embodiment, the head oscillates during grinding. Additional advances have occurred in the art since the invention in the cross-referenced application was made. For example, new head surface contours cannot be obtained by oscillating the head during grinding. Also, new applications for single-track heads make techniques utilizing bridges spanning two or more elements impractical. It has become necessary to monitor electric current through a single-track magnetic head while the head is continuously rotating about an axis passing through the surface being formed.
Single-track, thin film, batch-fabricated magnetic heads are known. Bajorek et al. in an article in the Oct., 1973, IBM TECHNICAL DISCLOSURE BULLETIN at page 1372, describe a single-turn magnetoresistive recording head incorporating copper or gold conductors. Landler, in an article in the May, 1969, IBM TECHNICAL DISCLOSURE BULLETIN, pages 1792-1793, suggests monitoring the resistance of an extra conductor, surrounding a single-turn head, during lapping until current conduction is interrupted or becomes discontinuous. Landler appears to require four external leads.
A rotatable fixture for a multitrack magnetic head is described in U.S. Pat. No. 3,681,682 (C. M. Cox and R. B. Fisher, filed Dec. 21, 1970, issued Aug. 1, 1972, and assigned to International Business Machines Corporation). This fixture connects each track's winding, in turn, to testing equipment including impedance measuring circuits. A continuously rotating two-terminal carbon resistor is monitored by a Wheatstone bridge in U.S. Pat. No. 3,105,288 (D. E. Johnson and J. L. Owens, filed Feb. 27, 1959, issued Oct. 1, 1963, and assigned to Western Electric Company, Incorporated). Each resistor terminal is connected to the bridge through a single slip ring brush combination. A Kelvin bridge (Dawes, Electrical Engineering, pages 169-170, McGraw-Hill, 1952) provides vastly greater accuracy than a Wheatstone bridge, but requires four connections for a two-terminal, unknown resistance. Slip ring assemblies having more than one brush per ring are commercially available.
Thus, there is no suggestion in the prior art of a unified solution to the problem of monitoring, during surface formation, current through a head while it is in continuous rotation about an axis through the surface being formed.